Dynamic low power states characterization

ABSTRACT

An optimal idle state of a processor is selected using dynamically derived parameters. For example, the idle state is selected from a group of possible idle power states. A current detector is arranged to perform power measurements of the processor and to report a total power consumption of the processor for each time value of a range of discrete values for each possible idle power state. A calibration unit is arranged to communicate with the current detector and the processor, and to automatically activate a calibration sequence that is used to produce data from which idle power state is optimal for the processor for an estimated idle period.

CLAIM OF PRIORITY

This application for Patent claims priority to EP PS Application No.13290183.6 entitled “DYNAMIC LOW POWER STATES CHARACTERIZATION” filedAug. 1, 2013 in the French Patent Office, wherein the application listedabove is incorporated by reference herein.

BACKGROUND

Increased integration of digital processors has led to processorarchitectures that provide increased functionality and processingcapabilities. The increased integration and increased functionality alsoleads to greater power consumption and/or power dissipation. Excessivepower consumption and power dissipation often limit the functionalityand battery-life of portable devices that incorporate processors. Forexample, the time duration of portable devices operating in an activemode is limited by the ability of portable power supplies (which can beexpensive, bulky, and heavy) to meet the power consumption demands ofthe portable devices. Likewise, minimizing heat build-up and energyconsumption are of concern even in many devices that are coupled to linepower.

SUMMARY

As disclosed herein, the problems noted above can be solved in largepart by informed selection of low power states of a device that are usedto save power. For example, the power consumption of a device in variouslow power states can be dynamically characterized and thecharacterization used to select a low power state that is optimal withrespect to the expected length of a quiescent period of the device.

A system for dynamic low-power characterization for power stateselection typically includes a processor coupled to a power supply, adetector, and a calibration unit. The operation of the processorincludes idle power states, where each idle power state is associatedwith an idle period. The detector is arranged to perform powerconsumption measurements of the processor and to report a total powerconsumption of the processor for each possible idle power state. Thecalibration unit is arranged to communicate with the detector and theprocessor, and to receive total power consumption-related data from thedetector. The calibration unit automatically activates a calibrationsequence to store threshold information that is used to select anoptimal low power state of the processor.

The threshold information is determined by repeating the calibrationsequence for different idle periods and for each low power state,comparing the received total power consumption data for each low powerstate for the different idle periods with total power consumption datafor each of the other low power states for the different idle periods,and selecting an optimal low power state for a given idle period basedon the total power consumption data reported by the detector. In someexample embodiments, the detector may be arranged in a substrate inwhich the processor is arranged.

This Summary is submitted with the understanding that it is not be usedto interpret or limit the scope or meaning of the claims. Further, theSummary is not intended to identify key features or essential featuresof the claimed subject matter, nor is it intended to be used as an aidin determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a computing device 100 inaccordance with preferred embodiments of the disclosure.

FIG. 2 is a block diagram illustrating a system having dynamic low-powercharacterization for power state selection in accordance with an exampleembodiment of the disclosure.

FIGS. 3 a and 3 b are graph diagrams that illustrate the total amount ofpower consumed by a processor over time in accordance with an exampleembodiment of the disclosure.

FIG. 4 is a graph that illustrates variations in total power consumptionfor various lengths of the different idle power states of a processor inaccordance with an example embodiment of the disclosure.

FIG. 5 is a flow diagram illustrating dynamic low-power characterizationfor power state selection in accordance with an example embodiment ofthe disclosure.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be example of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

Certain terms are used throughout the following description—andclaims—to refer to particular system components. As one skilled in theart will appreciate, various names may be used to refer to a componentor system. Accordingly, distinctions are not necessarily made hereinbetween components that differ in name but not function. Further, asystem can be a sub-system of yet another system. In the followingdiscussion and in the claims, the terms “including” and “comprising” areused in an open-ended fashion, and thus are to be interpreted to mean“including, but not limited to . . . . ” Also, the terms “coupled to” or“couples with” (and the like) are intended to describe either anindirect or direct electrical connection. Thus, if a first devicecouples to a second device, that connection can be made through a directelectrical connection, or through an indirect electrical connection viaother devices and connections.

FIG. 1 is a block diagram illustrating a computing device 100 inaccordance with preferred embodiments of the disclosure. For example,the computing device 100 is, or is incorporated into, a mobilecommunication device 129, such as a mobile phone, a personal digitalassistant, a personal computer, automotive electronics, projection(and/or media-playback) unit, or any other type of electronic system.

In some embodiments, the computing device 100 includes a megacell or asystem-on-chip (SoC). Computing device 100 may include control logicsuch as a CPU 112 (Central Processing Unit), a storage 114 (e.g., randomaccess memory (RAM)) and tester 110. Computing device 100 also includesa detector 134 (e.g., a current sensor) that is arranged to measurepower consumption of CPU 112 over time.

The CPU 112 can be, for example, a CISC-type (Complex Instruction SetComputer) CPU, RISC-type CPU (Reduced Instruction Set Computer), or adigital signal processor (DSP). For example, the CPU 112 can be aprocessor such as a microcontroller that is arranged in a commonsubstrate with the storage 114, tester 110, and the detector 134.

The storage 114 (which can be memory such as on-processor cache,off-processor cache, RAM, flash memory, or disk storage) stores one ormore software applications 130 (e.g., embedded applications) that, whenexecuted by the CPU 112, perform any suitable function associated withthe computing device 100. For example, calibration unit 132 can beimplemented using program and data information stored in storage 114that is processed by CPU 112.

The tester 110 is a diagnostic system and comprises logic (embodied atleast partially in hardware) that supports monitoring, testing, anddebugging of the computing device 100 executing the software application130. For example, the tester 110 can be used to emulate one or moredefective or unavailable components of the computing device 100 to allowverification of how the component(s), were it actually present on thecomputing device 100, would perform in various situations (e.g., how thecomponents would interact with the software application 130). In thisway, the software application 130 can be debugged in an environmentwhich resembles post-production operation (e.g., that occurs afterdeployment).

The CPU 112 comprises memory and logic that processes and/or (at leasttemporarily) stores information under control of programs accessed fromthe storage 114. The computing device 100 is often controlled by a userusing a UI (user interface) 116, which provides output to and receivesinput from the user during the execution the software application 130.The output is provided using the display 118, indicator lights, aspeaker, vibrations, and the like. The input is received using audioand/or video inputs (using, for example, voice or image recognition),and electro-mechanical devices such as keypads, switches, proximitydetectors, and the like.

The CPU 112 and tester 110 are coupled to I/O (Input-Output) port 128,which provides an interface that is configured to receive input from(and/or provide output to) peripherals and/or computing devices 131,including tangible (e.g., “non-transitory”) media (such as flash memory)and/or cabled or wireless media (such as a Joint Test Action Group(JTAG) interface). These and other input and output devices areselectively coupled to the computing device 100 by external devicesusing wireless or cabled connections. The CPU 112, storage 114, andtester 110 are also coupled to a programmable power supply 120, which isconfigured to receive power from a power source 136 (such as a battery,solar cell, “live” power cord, inductive field, fuel cell, and thelike).

As disclosed herein, a detector 134 is used to measure the powerconsumption of the SoC that includes the CPU 112. Detector 134 iscoupled to the SoC and arranged to measure total power consumption ofthe SoC for each given low power state of the processor. A low-powerstate is, for example, any power state during which power conservationis desired while operating a subset of components of the SoC. Detector134 can be a current sensor (such as a resistor) or an electromagneticfield sensor (such as an inductor) that is arranged to develop a voltagethat corresponds to the current being measured. In response, thedetector is arranged to provide indications of power consumption of theprocessor that are used to determine an amount of power consumed by theprocessor while in any C-state. To measure the total power consumptionof the SoC, detector 134 may be configured to convert the developedvoltage into a (e.g., digital) value that corresponds to theinstantaneous current measured. The power consumption can be determinedfrom the current measurements in accordance with the applied voltage,for example.

An application processor, such as a multimedia processor, is often themost power-consuming device in portable electronic appliances. Duringtimes of lesser or no activity, the processor may be programmed to enterlow power states (such as an idle state) in order to save energy. Eachprocessor typically has different levels of idle power states, such asan inactive mode, a retention mode, and an off mode. The differentlevels of power states are collectively called “C-states.” During idlepower states power is selectively decoupled from idle units inside theprocessor. Usually, greater energy savings are achieved when greaternumbers of components of the processor are halted.

A deep idle power state corresponds with very low power consumption. Asillustrated below with reference to FIG. 3 a and FIG. 3 b, a deep lowpower state typically requires more energy and longer transition periodsfor the processor to enter the idle power state and to emerge from theidle power state. Hence, an idle time can be predicted (e.g., based onprocessing requirements over a quiescent period), and an optimal powerstate can be selected based on various trade-offs between entry/exitsequences energy cost and idle power gain during the predicted idleperiod.

Conventionally, the different levels of power states (C-states) of aprocessor are determined through simulation and static calibration in anengineering laboratory. The optimal idle power states for a specificprocessor are found through laboratory-based characterization at a giventime (e.g., after manufacture and before deployment) and in apredetermined environment (e.g., room temperature). The C-state rankingis maintained throughout the life of the processor, even if some of theselected idle power states are no longer optimal as the processor agesover its operational lifetime.

As disclosed herein, a dynamic low power state calibration unit isarranged to dynamically measure actual current consumption during eachlow power state at various points in the lifetime of the computingdevice 100. The actual current consumption (e.g., after deployment atany point in the lifetime) can be measured using embedded and automatedprocess, and the current measurements can be used to refine and tunepower parameters that are associated with each C-state. Accordingly,power consumption for various C-states can be optimized at the productlevel for each device after deployment.

Software applications 130 can be used to implement (or be coupled to) acalibration unit 132. Calibration unit 132 is arranged to automaticallytrigger a calibration sequence to select the most optimal idle powerstate for CPU 112 that can be reached within a given idle time.Calibration unit 132 is arranged to collect, store, analyze, process,organize, and distribute data received from detector 134. In particular,calibration unit 132 performs a calibration sequence by varying idleperiods of CPU 112, storing power consumption data received fromdetector 134 for each idle period, comparing the stored data with a listof idle power states, and determining an optimal idle power state forCPU 112 for various ranges of idle periods based on the total powerconsumption reported by detector 134 for specific idle power statedurations. Calibration unit 132 can be arranged in a common (orseparate) substrate to form an integrated unit with the processor and/orthe detector. In other example embodiments, detector 134 and calibrationunit 132 can be arranged in assemblies separate from the computingdevice. The detector 134 can be arranged in a common substrate, forexample, that includes a processor that is arranged to performanalog-to-digital conversions.

FIG. 2 is a block diagram illustrating a system 200 having dynamiclow-power characterization for power state selection in accordance withan example embodiment of the disclosure. System 200 includes aprogrammable power supply 210 that is arranged to supply power to CPU220 (which is a processor such as CPU 112). CPU 220 includes powerdomains (e.g., power domains 222, 224, and 226) each of which is usedfor powering a selectable component of the CPU 220. The power domainsare individually selected to provide (or, alternately, deselected toconserve) power associated with a processing unit. The power consumed bythe processor 220 can be measured using the detector 230.

The calibration unit 240 is arranged to measure current consumption invarious low power states and store the results in C-state library 250.For example, the calibration unit is arranged to individual measure apower consumption of the CPU in each low power state (e.g., for use inselecting an appropriate low power state during actual operation). Theprogrammable power supply 210 and/or the CPU 220 are selectively enabledin accordance with each low power state that is to be characterized.

Each low power state 252 is characterized by measuring power-relatedparameters 254 (including, for example, the power used while entering,remaining in, and exiting a selected power state). The length of timeover which the CPU 220 changes power states can be measured using timer260. Likewise, the timer 260 can be used to control the length of timethe CPU remains in the idle period of a selected power state. Athreshold 256 is a duration that indicates a power state transitionthreshold that indicates an optimal power state that is used inaccordance with the duration of an estimated idle period. (As discussedbelow, various power states have varying efficiencies that depend on,for example, the length of time of the estimated idle period.)

In operation, the idle period estimator 270 is arranged to determine theduration of a period of quiescence (e.g., limited processing) inresponse to an operating state and/or conditions of the system 200. Whenthe idle period is estimated, the estimated idle period value iscompared with the threshold 256 values (e.g., to determine whether theestimated idle period value falls within a particular range defined bythe thresholds 256 values), and an optimal power operating state isselected in accordance with the comparison.

During idle periods that occur during normal operation (such as when theCPU is being used for an intended purpose that is different from thecharacterization process), the processor is selectively be programmed toenter lower power states (e.g., in order to save energy from beingexpended). In general, processors have several power saving statescalled C-states, which reflect the capability of an idle processor toturn off unused components (e.g., units, sub-processors, clock trees,power supplies, and the like) in order to save power.

The C-states are typically indicated with a number, for example C1, C2,C3 . . . Cn. The various C-states can be entered by gating clock signals(e.g., to prevent clock transitions), by cutting power from idle unitsinside the CPU 220, by reducing the CPU voltage supplied by theprogrammable power supply, and the like. In the state where a processorruns in the C0 state, the processor is considered to be activelyexecuting instructions. A processor running in any other C-state hascomponents that are idle and thus do not consume as much power as whenthe CPU 220 is actively executing instructions. The state C1 typicallyrefers to a power saving state wherein the internal CPU clock signal isstopped.

The higher the C number, the deeper the CPU sleep state (e.g., higher Cnumbers are used to describe situations where more components are shutdown to save power). While the deeper sleep states increasingly savemore power, greater latencies (e.g., transition times encountered whilechanging power states) are progressively encountered. In various exampleembodiments, a state can also have sub-states with different powersaving thresholds. Thus, the degree of depth of the low power state canbe progressively chosen to minimize latencies and power consumption.

Generally, each C-state has three periods associated with an idleperiod. For example, the entry transition period (e.g., save period) isthe period used for the processor to transition from an active to aninactive state. The quiescent idle time is the period between the end ofthe entry transition period and the beginning of the exit transitionperiod. The exit transition period (e.g., restore period) is the periodthat is used by the processor to transition from a wake-up event to theactive state.

FIGS. 3 a and 3 b are diagrams that illustrate the total amount of powerconsumed by a processor over time in accordance with an exampleembodiment of the disclosure. Graphs 300 and 302 show time (in units ofmilliseconds) on the x-axis and power (in units of mW) on the y-axis.

FIG. 3 a includes a graph 300 for illustrating a predefined idle powerstate 340 (Cx). Graph 300 includes blocks 310, 320, 330, and 340, eachof which reflects the amount of power consumed by the processor over adefined period of time. Block 310 represent the amount of energy used totransition to an active operating state. Block 320 represents the amountof energy used by a processor during the active operating state of theprocessor (e.g., when the processor is fully turned on). Block 330represents the amount of power consumed during a transition statewherein the processor transitions from the active operating state to lowpower state Cx. Block 340 represents a low power state wherein theprocessor is in the idle state Cx. Thus, block 310A represents theamount of energy that is needed to wake up the processor from low powerstate Cx, after which the processor reenters the operating staterepresented by block 320A. A further low power state can be entered assuggested by block 330A. Thus, the sequence of activity/inactivity canbe repeated over time.

FIG. 3 b shows a diagram 302 of another idle power state Cy of theprocessor illustrated in FIG. 3 a. Graph 302 includes blocks 312, 322,332, and 342, each of which reflects the amount of power consumed by theprocessor over a defined period of time. Block 312 represent the amountof energy used to transition to an active operating state. Block 322represents the amount of energy used by a processor during the activeoperating state of the processor (e.g., when the processor is fullyturned on). Block 332 represents the amount of power consumed during atransition state wherein the processor transitions from the activeoperating state to low power state Cx. Block 342 represents a low powerstate wherein the processor is in the idle state Cx. Thus, block 312Arepresents the amount of energy that is needed to wake up the processorfrom low power state Cx, after which the processor reenters theoperating state represented by block 322A. A further low power state canbe entered as suggested by block 332A.

Idle power state Cy is deeper than idle power state Cx, which isreflected by the lower power consumption encountered by the processorduring the more prolonged idle time of power state Cy. However, longeridle periods are needed to justify optimally transitioning into powerstate Cy (as compared with merely transitioning into power state Cx)because transition times are longer, as shown by blocks 310 and 330.Thus, matching the selected power state to the expected length of theidle time allows transitioning to the selected low power state using aminimum of power consumption overall.

Accordingly, a deeper idle power state is associated with longertransition periods, which entail higher energy costs while transitioninginto and out of the idle time periods. Depending on the predicted idletime, the most optimal idle power state is selected based on a trade-offbetween the entry and exit sequences energy cost and the idle powersaved during the quiescent idle period.

Selecting the most optimal idle power state from amongst differentpossible idle power states for a given idle time depends on the accuracyof the trade-off analysis. The trade-off analysis typically depends ofdifferent parameters, such as the SoC type, temperature, product type,and/or the type of application running on the device. Because of productaging (which, for example, produces gradual changes in junctioncharacteristics over the lifetime of the system 200) and differentperformance levels at differing operating temperatures, voltages, andsoftware applications, a calibration sequence is performed using (e.g.,as closely as possible) normal operating conditions (such as a during,or in-between, active processing).

As disclosed herein, the calibration unit performs a calibrationsequence to select the most optimal idle power states for the devicethat can be selected for a given (e.g., estimated) idle time. Thecalibration sequence determines characteristics for all the availableidle power states that are used to determine which power state is themost efficient (e.g., based on total power consumption) for a given idletime. The calibration process can be initiated in the field when duringboot, sleep, hibernate, shutdown modes, at periodic times, upon request,and the like. In some embodiments, the calibration unit engages anembedded current sensor (e.g., that is able to automatically perform thepower measurements during any change in power state) and store theresults in library 250. The calibration sequence can also be triggeredin the field each time a predetermined parameter changes. The parameterschanges can be a change such as a change in temperature or a change inperformance requirements of the application. For example the performancerequirements can be specified using units of operational performancepoints (OPPs) which, for example, indicate an amount of work beingaccomplished by a processor over a given time period.

FIG. 4 is a graph that illustrates variations in total power consumptionfor various lengths of the different idle power states of a processor inaccordance with an example embodiment of the disclosure. The graph 400illustrates four curves that represent power consumption profiles (e.g.,curves) of four different low power states of a processor, namely C1,C2, C3, and C4. Thus, for example, each point on a curve represents thetotal power consumed during an idle state when the duration of the idleperiod is (only) the length of the time value shown on the horizontalaxis.

The graph also illustrates threshold times, ThC2 and ThC4, whichrespectively correspond to thresholds associated with transitioning tolow power states C2 and C4. Each intersection between an initial C-stateprofile and a successive C-state profile determines a threshold timethat corresponds to a point at which there is a change in optimalC-state of the processor. Because the optimal state is defined as thelowest power consumption, the lowest portions of the power profilesdefine the optimal power states. Thus, the threshold time defines alength of an estimated idle time after which the named successiveC-state is most optimal.

For example, the threshold ThC2 is a time value (e.g., that correspondswith an idle time of about 7,500 μs) at which time the curves C1 and C2intersect. For idle times shorter than ThC2, C1 is determined as themost optimal C-state. For idle times longer than ThC2, C2 is determinedas the most optimal C-state. Between about 7,500 μs and about 30,000 μs,C2 is determined as the most optimal C-state for the processor. At about30,000 μs, curves C2 and C4 intersect (at the threshold ThC4) and thethreshold ThC4 indicates the idle time value at which there is a changein optimal C-state. Thus C-state C4 is defined as the most optimalC-state for idle time longer than around about 30,000 μs.

Each time a calibration sequence is triggered (e.g., during normalsystem operation), the embedded current sensor is arranged to provide apower consumption profile over each possible idle power state definedfor the processor. The embedded current sensor can measure theinstantaneous current at intervals sufficient to provide sufficientresolution of power profiles to provide a substantial power savings whenusing the disclosed dynamic characterization. A substantial powersavings is, for example, a power savings that is measurable.

During a calibration sequence, a software application (using timer 260,for example) can be used to vary the wakeup period of the centralprocessing unit, which determines the end of the idle period. (Forexample, a timer can be programmed using an adjustable terminal value toset the length of idle period.) At the end of the idle period, the powerconsumed (as measured over the length of the idle period) is aggregatedand used to plot a point on the curve. (Linear interpolation can be usedto approximate points for which no current measurements are made.)

A curve that illustrates the total power consumption of the processorfor different idle periods is generated for each possible idle powerstate. Superimposing and analyzing the generated curves for each idlepower state allows for determining the most optimal idle power state fora given range of idle periods. Accordingly, the calibration system doesnot require the use of an engineering laboratory for individualcharacterization of the different idle power states. Instead, theselection and the ranking of the different idle power states areprocessed automatically by a dynamic process in the calibration unit. Insome embodiments, the system may reduce the number of low power statesthat are characterized by characterizing only the most optimal idlepower states (e.g., by performing the characterization on only the idlestates having the lowest curve segment in between threshold times ofFIG. 4), which reduces the time and power required for power statecharacterization.

FIG. 5 is a high-level flow diagram illustrating dynamic low-powercharacterization for power state selection in accordance with an exampleembodiment of the disclosure. A calibration sequence 500 performed by acalibration unit (such as calibration unit 240) can be implemented inhardware and/or in various combination of software and hardware.Calibration sequence 500 includes a data collection process performed inoperations 510 to 570, storage of recorded measurements in operation580, and a sorting process arranged to select the most optimal C-statesin operation 595 and to provide an updated optimized list of C-states inoperation 595.

The calibration sequence is initiated at operation 510 wherein a list ofdata of possible low power states (C-states) for the processor isparsed. The parsed information includes, for example, informationsufficient to identify each particular low power state to becharacterized and to induce the processor to enter an identifiedparticular power state each occasion process 510 is entered. Eachparticular low power state that is characterized is added to a group ofthe characterized idle states. The process proceeds to operation 520.

In operation 520, the calibration sequence is provided with a value thatis used to increment the duration of an idle time to be used forcharacterizing an idle state. For example, the idle time can be set toincrease in increments of 100 μs such that each successive iteration ofoperation 530 has a duration that is 100 μs longer than the previousiteration. The increment is set finely enough to provide accurate powerprofiles while not incurring excessive processing requirements (such asOPPs and power) during characterization. Program flow continues inoperation 530.

In operation 530, the total current of the process measured (by thecurrent detector) in response to the expiration of the elapsed idletime. The total current (which can be used to determine the total power,and vice versa) can be determined by aggregating current measurementsperformed throughout the idle period. The measurement of the totalcurrents includes the transition time to enter and exit the idle periodas well as the power consumed in the idle period itself. Thus, eachcharacterized idle state is characterized by determining an aggregateamount of power consumed by the processor during each iteration (e.g.,when the processor is operating in the idle state being characterizedfor different idle periods). In some example embodiments, the totalcurrent can include measurements that occur during one or more of theentry transition period, the quiescent idle period, and the exittransition period. Program flow continues in operation 540.

In operation 540, data sets reflecting the current measurements arestored. In particular, for a given idle power state (C-state) and agiven idle time (incremented), the aggregate current measurementsprovide an indication of the total power consumption of the processor(e.g., over the period of time over which the samples are aggregated),and the power consumption data are stored. Program flow continues inoperation 550.

In operation 550, idle times are compared to a maximum idle time todetermine whether all data points have been produced for the identifiedparticular power state. If a maximum idle time has not yet been reached,the sequence returns to operation 520 where the idle time isincrementally increased (and another data point is produced). Thesequence proceeds with the new idle time through operations 530, 540 and550. The operational process is repeated until the maximum idle time isreached. When the maximum idle time is reached, program flow continuesin operation 560.

In operation 560, the sequence verifies whether the last (e.g., deepest)power state has been reached. For example, if the sequence has performedoperations 520 to 560 with a high power state (such as C2 state), thesequence returns to operation 510 and repeats operations 520 to 560 bycharacterizing a deeper power state (for example C3). The sequencerepeats until the last power state has been characterized, and programflow continues in operation 570.

In node 570, the data collection portion of the calibration sequence hasended. Program flow continues in operation 580. wherein eachcharacterized idle state is characterized by determining an aggregateamount of power consumed by the processor of each iteration when theprocessor is operating in the idle state being characterized fordifferent idle period

In operation 580, data retrieved from the data collection process arerecorded for post-measurement analysis. Program flow continues inoperation 590.

In operation 590, C-states are sorted based on an algorithm that findsoptimal C-states and associate threshold times. The algorithm beginswith selecting C1 as the highest power state and determining a thresholdTh1 that is a value that is around the minimum idle path latency. Thealgorithm compares relative power consumption (Cn) of each power profileat each idle time point. The comparison can proceed from the highest tothe deepest power state and from the shorter to the longer idle times.Thus, the comparison identifies the power profile (e.g., power state)having the lowest power consumption at each value of idle times. Theoptimal idle power state and threshold times are verified and sorted todetermine the power state transition thresholds (such as ThC2 and ThC4as discussed above with respect to FIG. 4.)

The process is repeated (e.g., in operation 590) until all C-states aresorted with corresponding updated threshold times (which reflect changesof one optimal C-state to another optimal C-state). Thus an optimal idlestate can be selected in response to the characterized idle states by(for example) using an estimated idle period (in which the processor isestimated to remain in the selected idle state) as an index forcomparing with the thresholds and determining the particular C-statethat is associated with the threshold have the same (or closest lower)value as the estimated idle period.

Program flow terminates in operation 595 by providing an optimized list(e.g., C-state library 250) of C-states and corresponding thresholdtimes (such as thresholds 256). As discussed above, the provided list isused to select a power state that is optimal for time in which aprocessor (or component thereof) is expected to be quiescent.

By automatically performing a calibration sequence (e.g., during normaloperation after deployment), the system can compensate for progressivelyoccurring changes in idle power states, for example due to changes inprocess performance, device aging, or changes in process distribution,without soliciting user input. In some example embodiments, thecalibration unit may repeat the calibration sequence periodically. Inother example embodiments, a list of selected idle power states andtheir associated idle periods in the calibration unit may be updatedbased on a change in one or more predetermined parameters. For example,predetermined parameters that trigger the calibration sequence in thefield may include a product type in which the computing device is used(for example a mobile phone, a personal digital assistant, a personalcomputer, automotive electronics, or a projection (and/ormedia-playback) unit), a type of computing device (for example asystem-on-chip, such as multimedia application processor), a particularapplication running on the computing device, a substantial temperaturechange of the computing device (e.g., a temperature change that wouldresult in the power state transition thresholds) and/or by performancerequirements of the computing device (for example, a change in anoperating performance point).

The disclosed calibration system optimizes power consumption of adevice. For example, in some multimedia use cases implementation of thecalibration system can result in power savings of up to 30 percent.Additionally, the actual power consumption of a computing device orprocessor may vary in accordance with a particular customerimplementation. Implementation of the disclosed calibration systems,devices, and methods may be adjusted to specific customer products byproviding (e.g., after deployment of the specific product) a parsablelist of possible idle power states for the specific product. In someembodiments the list may be modified, in other embodiments the list maybe repeated, either partially or entirely. The parsable list of possibleide power states need not provide a ranking of the different idle powerstates. In some embodiments, the calibration system may take advantageof already-implemented debug structures used for power optimization, forexample as present in tester 110.

Although the system is described in terms of using a processor, thedynamic calibration unit also can function with or without the use ofprocessor logic. The dynamic calibration unit can be implemented inhardware and/or in various combinations of software and hardware. Insome example embodiments, the current detector may be arranged in asubstrate that includes the computing device. In other exampleembodiments, the current detector may be arranged in a differentsubstrate. In further example embodiments, the current detector may be acomponent that is distinct from the computing device.

In some example embodiments, a current detector may be integrated in apower-management device. In further example embodiments, a dynamiccalibration unit may be included in the current detector (for example acurrent detector may include an internal storage facility and softwareto execute the functions of the calibration unit). In further exampleembodiments, a current detector may store data and the functions of thecalibration unit may be executed on a different device that is coupledto the processor for which optimal power states are selected.

The disclosure further contemplates methods for characterizing low powerstates. In some embodiments, the method may include coupling a processorto a power supply, the processor including a plurality of idle powerstates, and with each idle power state associated with an idle period. Acurrent detector may be coupled to the processor. The detector may bearranged to perform total power consumption measurements of theprocessor. A calibration unit may be coupled to the detector and theprocessor, and the calibration unit may be arranged to automaticallyactivate a calibration sequence to select an optimal idle power state ofthe processor based on receiving total power consumption data from thedetector for each idle period, comparing the received total powerconsumption data with stored total power consumption data for each idlepower state, repeating the process for different idle periods, andselecting an optimal idle power state for a given idle period. In someembodiments, the calibration sequence is activated by one or morepredetermined parameters. In further embodiments, the calibration unitincludes a list of selected idle power states and their associated idleperiods, and the list is updated automatically. In some embodiments, thecalibration unit determines a threshold time associated with changes inoptimal idle power states and the threshold time is updatedautomatically.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the claimsattached hereto. Those skilled in the art will readily recognize variousmodifications and changes that could be made without following theexample embodiments and applications illustrated and described herein,and without departing from the true spirit and scope of the followingclaims.

What is claimed is:
 1. A computing device, comprising: a processor thatis arranged to enter an idle state that is selected from a group ofcharacterized idle states, wherein the selected idle state is an optimalidle state that is selected from the group of the characterized idlestates in response to an estimated idle period in which the processor isestimated to remain in the selected idle state; a detector that isarranged to provide processor power indications that are used todetermine an amount of power consumed by the processor while theprocessor is in any of the idle states of the group of characterizedidle states; and a calibration unit that is arranged to characterizeeach idle state of the group of characterized idle states in response tothe provided processor power indications, wherein each idle state ischaracterized by determining an aggregate amount of power consumed bythe processor during each iteration of the processor operating in theidle state for a different idle period.
 2. The device of claim 1,wherein the calibration unit is arranged to compare an aggregate powerconsumption for each different idle period of a plurality ofcharacterized idle states of the group of idle states and select an idlestate having the least aggregate amount of power that is associated withthe estimated idle period.
 3. The device of claim 2, wherein thecalibration unit is arranged to compare each aggregate power consumptionfor each different idle period of a first characterized idle state witheach aggregate power consumption for each respective different idleperiod of a second characterized idle state and determine a thresholdwhere one of the aggregate power consumption for each different idleperiod of either the first or second characterized idle statestransitions to a power consumption that is lower than a respectiveaggregate power consumption of the second or first, respectively,characterized idle state.
 4. The device of claim 3, wherein thecalibration unit is arranged to store the determined thresholdinformation in association with an indication of the idle state havingthe transitioned-to lower power consumption, wherein the indication ofthe idle state identifies the idle state having the transitioned-tolower power consumption as being the optimal idle power state.
 5. Thedevice of claim 4, wherein the estimated idle period is compared withthe stored threshold information to determine the associated idle statehaving the lower power consumption.
 6. The device of claim 4, whereinthe indication of the idle state identifies the idle state having thetransitioned-to lower power consumption as being the optimal idle powerstate.
 7. The device of claim 6, wherein the optimal idle power state issubsequently characterized in response to the identification of beingthe optimal idle power state.
 8. The device of claim 1, wherein thecharacterization is performed after the deployment of the computingdevice.
 9. The device of claim 8, wherein the characterization isinitiated within the computing device.
 10. The device of claim 1,wherein the stored threshold information is updated to reflect newerthreshold information derived from the processor power indicationsprovided by the detector.
 11. The device of claim 1, wherein thecharacterization is performed at periodic intervals.
 12. The device ofclaim 1, wherein the characterization is performed in response to achange in operating temperature of the computing device.
 13. The deviceof claim 4, wherein estimation of idle time is determined in response toa comparison between performance requirements and performancecapabilities of the computing device.
 14. The device of claim 1, whereinthe idle period includes the quiescent idle period and one or more ofthe entry transition period and the exit transition period of the idlestate.
 15. A low power states characterization system, comprising: aprocessor coupled to a power supply, the processor including a pluralityof idle power states, each idle power state associated with an idleperiod; a current detector that is arranged to perform powermeasurements of the processor and to report a total power consumption ofthe processor for each possible idle power state over a plurality ofdifferent durations for each possible idle power state; and acalibration unit that is arranged to communicate with the currentdetector and the processor, and to store the reported total powerconsumption data from the detector, and wherein the calibration unitactivates a calibration sequence to select an optimal idle power stateof the processor in response to comparisons of the received total powerconsumption data with the stored total power consumption data for eachidle power state, repeating the calibration sequence for different idleperiods over each idle power state, and selecting an optimal idle powerstate for a given idle period in response to the total power consumptiondata reported by the current detector.
 16. The system of claim 15,wherein the current detector is arranged in a common substrate theprocessor.
 17. The system of claim 15 wherein the calibration unit is atleast partially embodied as a software application of the processor. 18.A method, comprising: selecting an idle state as an optimal idle statefrom a group of the characterized idle states in response to anestimated idle period in which a processor is estimated to remain in theselected idle state; providing processor power indications that are usedto determine an amount of power consumed by the processor while theprocessor is in any of the idle states of the group of characterizedidle states; and characterizing each idle state of the group ofcharacterized idle states in response to the provided processor powerindications, wherein each idle state is characterized by determining anaggregate amount of power consumed by the processor during eachiteration of the processor operating in the idle state for a differentidle period.
 19. The method of claim 18, comprising updating a list ofselected idle power states in response to a parsable list of possibleidle power states that is received after deployment of a system thatincludes the processor.
 20. The method of claim 18, wherein each idlestate of the group of characterized idle states is characterized afterdeployment of a system that includes the processor.